Preheat the oven to 350 F. Lightly grease the bottom of a 9x13 inch baking pan and line it with parchment paper. Set it aside.
In a medium mixing bowl, combine the flour, baking powder, and baking soda. Set aside.
In a large mixing bowl using a hand mixer on medium-high speed, cream the butter and both sugars together.
Add in the eggs, vanilla, and salt and mix on medium speed until just incorporated.
Slowly add the flour mixture and mix until you get a cookie dough consistency. Then fold in 1 cup chopped Reese’s peanut butter cup minis, ¾ cup semisweet chocolate chips, and ¼ cup chopped walnuts until evenly distributed in the dough. Set the remaining aside for topping.
Spread and press the cookie dough down into an even layer in the prepared baking pan. Sprinkle on the remaining toppings and lightly press them in so they stay in place.
Bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean.
After baking, leave the bars in the pan and set it on a wire rack. Allow it to cool at room temperature before cutting into squares and serving.
Notes
You can use regular sized Reese’s peanut butter cups if you like. Just roughly chop them into smaller chunks. Swap out the nuts with whichever is your favorite.Make sure that the ingredients come to room temperature before mixing. This will help it mix easier and incorporate much more evenly.Allow the bars to cool completely at room temperature before slicing. This will help give the bars time to firm up and get you the neatest slices.STORING
The dough can be made ahead and kept covered in the refrigerator for 2-3 days. Any longer and the dough will begin to dry out.Store leftover baked cookie bars in an airtight container as soon as they are cooled. They will keep on the counter for up to 3 days.Freeze leftover bars by slicing them into squares and stacking them in a freezer safe airtight container or bag with parchment paper between each slice for up to 3 months.